Just when all was well with my wife's 1986 740 turbo (154K)...

Last week, I was driving the car daily and noticed that the engine was idling rougher and rougher every day...and about mid-week, noticed that the engine would occasionally make a very loud clacking noise (right at cold start, or sometimes when cranked going up a hill, but gradually over the week, the clacking noise became louder and more constant). I checked the oil level as a first thing and noticed that the dipstick was coated all the way up the shaft with a tan frothy liquid. The car had just had an oil change three days before I saw this on the dipstick, so it could have been clean oil.

I stopped driving the car immediately. Having had similar symptoms with another brick that quickly evolved into a blown head gasket (I figured this froth was coolant mixed with oil), I wasted no time in pulling the head and replacing the gasket in this 740T. All back together now, and with new timing belt and re-sealed injectors to boot.

However, on first start with all new oil, etc., the clacking noise is quite bad and in just a minute of operation, the frothy stuff is back on the dipstick. I assume that this is a bad exhaust valve....but I've never done valves before in 10 years of maintaining my fleet of Volvos...

How do I check which one? It sounds like the clacking is coming from the 3rd or 4th cylinder, both of which had a little flaky crud in them when I opened up the engine...

And what to do about it? I've read the Bentley bible on this part and it sounds like a real job to reseal or replace valves...

Thanks!